MXPA06000078A - Electrical power generation system and method - Google Patents

Abstract

An electrical power generating system (10) and method wherein a generator (30) is driven by an air-breathing engine (20). At any operating condition, for a given power output the engine efficiency is substantially optimized by controlling the rate of air flow through the engine in such a manner that the fuel/air ratio is controlled to maintain a high peak temperature imparted to the working fluid in the engine. The method and system of the invention eliminate the need for variable-geometry mechanisms in the engine, and also eliminate the need for variable-geometry combustors and pre-burners. The invention is applicable to various types of air- -breathing engines that operate at low fuel/air ratios.

Description

WO 2005/003521 Al lllll llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll lili lili lili Published: For two-letter codes and o? Ier abbreviations. Refer to the "Guid¬ - with intemational search repon ance Notes on Codes and Abbreviations "appearing at ihe begin- - before tlie. Expiralion of l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l SYSTEM AND GENERATION METHOD PE ELECTRICAL ENERGY TECHNICAL FIELD OF THE INVENTION This invention relates to the generation of electric power using an air breathing motor to control a generator, which produces electric current for the supply to a load. In particular embodiments, the invention relates to the generation of electrical energy using a generator driven by means of a small turbine engine.

BACKGROUND OF THE INVENTION The generation of distributed energy is a concept that has been the subject of great discussion over the years, although to date there has not been a generalized development of distributed generation systems. Distributed generation means the use of small electric power generation systems located in the places where energy is required and, therefore, must be differentiated from the system of the traditional energy distribution network, where a large power plant The power plant produces energy that is then transmitted over substantial distances to a plurality of users through a system of power transmission lines commonly referred to as a distribution network. In contrast to conventional power plants operated by power distribution networks, which can often produce several megawatts of power, distributed generation systems generally have a capacity of less than two megawatts and, more generally, within the scale of 60 to 600 kilowatts. The fact that distributed generation has not achieved widespread development can be attributed primarily to cost. In most areas of the United States and, indeed, in much of the world, it has simply been more economical for most users to purchase power from a distribution network than to invest and operate a distributed generation system. An important factor that determines the relatively high cost of the energy of the distributed generation systems has been the relatively low efficiency of the small motors used in these systems, particularly in conditions of partial load operation. Typically, the generator in a distributed generation system is controlled by a small turbine engine, often called a microturbine or miniturbine, depending on the size. A turbine engine generally comprises a combustor for combusting fuel and mixing air to produce hot gases by converting the chemical energy of the fuel into heat energy, a turbine that expands the hot gases to rotate an axis on which the gas is mounted. turbine, as well as a compressor mounted on or coupled to the shaft and that can be operated to compress the air that is supplied to the combustor. Given the relatively low amount of electrical energy required from a distributed generation system, the turbine engine is equally small. For reasons related to the aerodynamics that occurs within the engine and for other reasons, the efficiency of a turbine engine tends to be reduced while the size of the engine is smaller. Accordingly, microturbines and miniturbines automatically have a disadvantage of efficiency with respect to larger engines. Additionally, regardless of size, the partial load efficiency of a turbine engine is notoriously bad, generally due to the particular manner in which the engine is operated under partial load conditions. More particularly, it is a typical case in turbine engines that the turbine inlet temperature, which basically represents the peak temperature of the operating liquid in the engine's cycle, drops as the engine's power output drops below the point of "design". The design point is generally a load condition with a 100 percent capacity and the motor is generally designed so that its peak efficiency basically occurs at the design point. It is well known that the main variable that influences the efficiency of the thermodynamic cycle of an engine is the peak temperature of the operating liquid. Everything else being the same, the higher the peak temperature, the greater the efficiency; conversely, the lower the peak temperature, the lower the efficiency. Therefore, if operating in a partial load condition, the motor is controlled in such a way that the peak effective temperature of the liquid operating in the cycle (i.e., the turbine inlet temperature) is substantially lower than that in the point of design, the efficiency of the engine tends to shrink to a substantial degree. In some gas turbines of the prior art, particularly the gas turbine engines of propulsion aircraft and the large gas turbines for electric systems of constant speed, variable geometry systems have been used in conditions of partial load to reduce the air flow, so that the efficiency of the engine is not impaired improperly. For example, variable input guide vanes (IGVs) have been used in axial flow compressors. In conditions of partial load, the IGVs are closed to reduce the air flow for a given compressor speed. In the case of radial compressors, the stator blades have sometimes become variable to achieve a similar effect. In still other cases, the variable first stage turbine nozzles or vanes have been used to control the speed of the turbine and, therefore, the speed of the compressor, so as to control the air flow rate. Such variable geometry systems are costly and the bearings and other removable components are prone to wear, making these systems impractical for electric power generation systems that must be available for service during a high percentage of hours per day , they must be able to operate basically continuously if required and must also be able to respond quickly to the energy changes required by the load being supplied. Additionally, the mechanisms of variable geometry are not practical to be implemented in microturbines and miniturbines due to the small size of the motor. Therefore, there is a need for counter with an alternative to variable geometry methods to optimize the performance of the engine under partial load conditions. Emissions (including, but not limited to, oxides of nitrogen, hydrocarbons not subject to combustion and carbon monoxide) represent another aspect of distributed generation that has proved to be a challenge. In general, for a given energy output, NOx emissions tend to be reduced or minimized by minimizing the fuel combustion temperature (also known as the flame temperature), which is generally higher than the peak thermodynamic temperature ( turbine inlet), thus reducing the production of nitrogen oxides without adversely affecting efficiency. The main method to reduce the flame temperature is to pre-mix the fuel and the air before the combustion zone produces a mixture with a relatively high proportion of fuel with respect to the air, ie a light mixture. Premixing also ensures that the temperature along the flame zone is almost uniform without hot spots that can lead to local NOx production. However, as the mixture becomes lighter, carbon monoxide (CO), unburned hydrocarbon (UHC), as well as pressure fluctuations are increased. . These trends continue and the flame zone becomes more instable as the mixture becomes even lighter, until the lightness extinction limit is reached. For any mixture that is lighter than this limit, no flame can be maintained. In practice, carbon monoxide and hydrocarbon emissions not subjected to combustion and / or pressure pulsations become unacceptably high before the lightness extinction limit is reached. The limit of extinction of lightness can be displaced to lighter regimes by increasing the temperature of entry to the combustor and using catalytic combustion. The use of catalytic combustion greatly increases the operating regime for light premixed combustion, producing a very low emission of NOx, as well as acceptable CO and UHC emissions and basically no pressure pulsation. However, catalytic combustion introduces another restriction in the operation called the lower catalytic activity limit. The entry temperature to the catalytic combustor must be maintained above this limit to maintain catalytic combustion. In many conventional microturbines, the motor control is such that, in conditions of partial load, the inlet temperature of the combustor tends to fall and the air / fuel mixture becomes lighter. In the case of conventional light premixed combustion, this tends to produce higher emissions. In the case of catalytic combustion, the downstream inlet temperature of the combustor can lead to failure to maintain catalytic combustion. In practice, catalytic and lightweight premixed combustors are able to operate only through a portion of the gas turbine's loading scale due to the incoming inlet temperature of the combustors and the increasingly light conditions prevailing at as the load is reduced. In some cases pre-combustors have been used before the combustors to trigger the combustor inlet temperature. Additionally, variable geometry combusers have been used in which a portion of the air is diverted around the combustor to maintain the fuel / air ratio at a level that allows for operational stability. The pre-burner solution poses a cost of reliability as excess temperature or other pre-burner malfunction can damage the main burner and also adds to the cost of the system. In addition, it imposes an operating cost as a result of the pressure loss that occurs through the pre-burner. This pressure loss is experienced even when the pre-burner is not in use. Variable geometry can be applied to eliminate the cost of pressure loss in addition to its use to maintain the fuel / air ratio. However, variable geometry solutions are costly, complicated and prone to excessive wear, downward reliability and increasing maintenance costs.

For many potential users, these factors have combined to make the generation of electric power through distributed generation systems less attractive than acquiring energy from large power distribution networks.

BRIEF DESCRIPTION OF THE INVENTION The present invention addresses the above needs and achieves other advantages by providing a system and method of generating electrical power where, under any operating condition, for a given power output, the efficiency of the motor is optimized considerably by controlling the air flow to through the engine, such that the fuel / air ratio is controlled to maintain a high peak temperature imparted to the operating liquid in the engine. The method and system of the invention eliminate the need for counter with variable geometry mechanisms in the engine, eliminate the need to have variable geometry combusers and also minimize the need to have pre-breakers. The invention is applicable to various types of air breathing engines operating under low fuel / air ratios including, but not limited to, rotary engines such as turbine engines and reciprocating engines such as free piston engines. In accordance with one aspect of the method of the invention, a method is provided for improving the partial load efficiency of an air breathing motor in an electric power generating system. The system has a movable shaft that communicates mechanically with the engine and a fuel system coupled with the engine and that can be operated to supply fuel to the engine at a controlled fuel flow rate. The engine is designed so that the peak thermodynamic efficiency of the engine substantially coincides with a load operating condition of 100 percent of the engine. The system includes an electric generator coupled with the shaft so that the movement of the shaft through the motor causes the generator to operate to create an alternating electrical current and the motor, shaft and generator are connected so that a change in speed of the generator causes a corresponding change in the engine speed and, therefore, a change in the air flow through the engine. The method comprises the steps of operating the motor under a partial load condition, as well as controlling the speed of the generator under the condition of partial load so as to control the air flow through the motor, while controlling simultaneously the fuel flow rate to the engine to control the fuel / air ratio, such that a peak cyclic temperature of the engine is basically the same as the peak cyclic temperature corresponding to the load operation condition of 100 percent. In other words, the cyclical temperature is not allowed to fall to any substantial degree by reducing the load below the 100 percent load condition (although under very low load conditions the peak cyclic temperature can be allowed to fall, such and as described in more detail below). This is achieved by controlling the fuel / air ratio, primarily through the control of the air flow through the engine. Since the air flow rate is a function of the motor speed, the air flow can be controlled by controlling the speed of the generator. In one embodiment, the step of controlling the generator speed comprises controlling a level of electrical current downstream of the generator. This can be achieved by converting the alternating current of the generator into a direct current and then converting the direct current into an alternating current at a fixed frequency independent of the generator speed. The fixed-frequency alternating current would then be supplied to the load. Using active current control in the conversion of alternating current (AC), for its acronym in English) to direct current (DC, for its acronym in English), the level of direct current is controlled so as to control the speed of the generator. For example, at a basically constant fuel flow rate, by reducing the direct current, a reduction of the load on the shaft occurs and, therefore, the generator is accelerated so that the output voltage is increased to maintain a balance general energy Conversely, increasing the direct current increases the load on the shaft so that the generator decelerates. When a winding generator with an excitation system is employed, the control of the speed of the generator can be achieved at least partially by controlling the excitation system. Alternatively, the speed of the winding generator can be controlled by controlling the AC / DC converter as indicated above or a combination of controlling the excitation system and controlling the AC / DC converter can be used. In another embodiment of the invention, a recuperator is used to preheat the air that is mixed with the fuel or to preheat the air-fuel mixture. The recuperator causes thermal exchange between the air or mixture and the exhaust gases discharged from the engine. Under very low partial load conditions, if the peak cyclical temperature was maintained at the same level as the 100 percent load point, the The temperature of the exhaust gases that enter the recuperator could exceed a maximum allowed value (dictated by material limits, for example). Accordingly, according to the invention, under said conditions, the speed of the generator is controlled so that the air flow through the engine is controlled and the fuel / air ratio is controlled in this way that the peak cyclic temperature is allowed to fall below the peak cyclic temperature corresponding to the 100 percent load operation condition. Accordingly, the temperature of the exhaust gases entering the recuperator does not exceed the predetermined maximum allowed value. In another aspect of the invention, the fuel is subjected to combustion in a catalytic combustor having a predetermined minimum inlet temperature required to maintain a catalytic reaction in the combustor. In many conventional motor control schemes, the inlet temperature of the combustor tends to fall as the engine load is reduced below the 100 percent load condition. Accordingly, it is possible that the temperature falls below the minimum temperature required for the catalytic reaction. According to the invention, the fuel / air ratio is controlled in such a manner, under partial load conditions, that an inlet temperature to the combustor is at least as large as the predetermined minimum inlet temperature. In one embodiment, the fuel / air ratio is controlled in such a way that the inlet temperature to the combustor, under a partial load condition, is greater than the inlet temperature, to the combustor under the 100 percent load condition. A system for generating electrical power for supply to a load, according to one embodiment of the invention, includes an air breathing motor that communicates mechanically with a movable shaft. An electric generator is coupled to the shaft so that the movement of the shaft through the motor causes the generator to operate to create an alternating electric current. The motor, shaft and generator are connected in such a way that a change in the speed of the generator causes a corresponding change in the speed of the motor and, therefore, a change in the air flow through the motor. The system also includes a system coupled fuel with the engine and can be operated to supply fuel to the engine, the fuel system having responsiveness relative to a control signal of fuel to vary a rate of fuel to the engine, and as at least one motor sensor being operable to measure at least one thermodynamic variable associated with the motor which is indicative of a relative thermodynamic efficiency of the motor. An electronic power unit is coupled to the generator to receive the alternating electrical current from that location and synthesize a alternating output current at a predetermined frequency for supply to the load. The unit power electronics in one embodiment comprises a module AC / DC structured and arranged to operate through alternating electrical current from the generator, so that a non-alternating direct current at a non-alternating voltage occurs, and a DC / AC module structured and arranged to operate through non-alternating direct current, so as to synthesize an alternating output voltage and current at a predetermined frequency and relative phase for supply to the load. In one embodiment, the AC / DC module may be responsive so that a current control signal varies the level of the non-alternating direct current regardless of the alternating electrical current of the generator. The system also includes a generator power sensor that can be operated to measure the energy output of the system, as well as a charge sensor that can be operated to measure the energy demanded by the load. A controller is operatively connected to the fuel system, to the at least one motor sensor, to the power electronics unit, to the generator power sensor and to the load energy sensor. The controller can be operated to control the fuel system, so that it causes the power output of the system to basically match the energy demanded by the load and, at the same time, controls the speed of the generator so as to control the speed of the generator. motor (and, therefore, the air flow rate), such that the fuel / air ratio of the mixture subjected to combustion in the engine is controlled to substantially maximize the relative thermodynamic efficiency of the engine. The control of the generator speed can be achieved by controlling the non-alternating direct current level of the AC / DC module of the power electronics unit, in the case of an actively controllable AC / DC module. In another embodiment in which the generator is a winding generator having an excitation system, the control system can be operated to control the excitation system, so as to control the speed of the generator and, therefore, the flow rate. of air. In a system such as that described above, another method according to the invention comprises the steps of: determining an energy demanded by the load; measure at least one thermodynamic variable associated with the engine that is indicative of a relative thermodynamic efficiency of the engine; control the supply of fuel to supply fuel to the engine at a controlled fuel flow rate, so that the electrical power output of the system basically matches the energy demanded by the load; and controlling the air flow through the motor independently of the electrical power output of the system, so as to control the fuel / air ratio of the mixture subjected to combustion in the engine, in such a way that it is substantially optimized the thermodynamic efficiency of the motor, the same time that the energy demanded by the load is basically matched, the air flow being controlled by electrically controlling the speed of the generator and, therefore, the air flow through the motor.

BRIEF DESCRIPTION OF THE DIFFERENT VIEWS OF THE DRAWINGS Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and in which: Figure 1 is a diagrammatic view of a power generation system in accordance with a modality of the invention. Figure 2 is a plot of temperatures at different points of the engine as functions of the relative generator load, comparing a control method of the prior art (dashed lines) with a control method according to an embodiment of the invention (lines continuous). And Figure 3 is a graph of the fuel / air ratio compared to the relative generator load, comparing a control method of the prior art (dotted line) with a control method in accordance with an embodiment of the invention (FIG. continuous line).

DETAILED DESCRIPTION OF THE INVENTION The present inventions will be described in more detail below with reference to the accompanying drawings which show some, though not all, of the embodiments of the invention. In fact, these inventions can take many forms of different modalities and should not be construed as limited to the modalities set forth herein. Instead, these modalities are provided so that the description meets the applicable legal requirements. Similar numbers refer to similar elements throughout it. An electrical generator system 10 in accordance with one embodiment of the invention is schematically shown in Figure 1. The system includes an air breathing motor 20 which combusts a mixture of fuel and air to produce hot combustion gases that they then expand to create mechanical energy. In the illustrated embodiment, the engine comprises a turbine engine having a compressor 22 mounted on one end of a rotary shaft 24, a turbine 26 mounted on the other end of the shaft and a combustor 28 for combustion of the fuel mixture / air. The combustor may be of different types including, but not limited to, one of diffusion, catalytic, light premixed flame and others. A mixture of fuel and air is supplied to the combustor. The air is first pressurized by the compressor. The fuel / air mixture is combusted in the combustor and the hot combustion gases are supplied to the turbine, which expands the gases, causing the turbine to be rotationally controlled. In turn, the turbine rotates the shaft, which controls the compressor. The system includes an electric generator 30 in communication with the shaft 24, such that the movement of the shaft causes the generator to be controlled. In the illustrated embodiment, in which the shaft is rotatable, the generator is likewise rotatable and the rotational movement of the shaft is imparted to the generator. The generator can be mounted directly on or connected to the shaft, so that there is a one-to-one speed ratio between the shaft and the generator or, alternatively, the generator and shaft can be connected through a gear train or similar, so that there is a different speed relationship. It is also possible that the shaft is swinging instead of rotating and that the generator is either reciprocating or rotating. In any case, the speed at which the generator operates dictates the speed of the axis and, therefore, the speed at which the engine operates. The generator 30 can be of different types, including permanent shaft generators, winding generators or combinations thereof. The generator produces an alternate voltage and electric current. As described in more detail below, in the illustrated mode, the alternating electric current of the generator is operated by power electronics to produce an alternating voltage and output current at a predetermined fixed frequency and phase relationship for supply to a load. The system 10 also includes a fuel system for supplying fuel to the combustor 28. The fuel system generally includes a fuel pump (not shown) and a fuel metering valve 32 that can be controlled by means of a suitable control signal 34., so as to control the fuel flow. A control system 40 is connected to the fuel metering valve 32 to control its operation. The control system also performs other functions, as described in more detail below. The system 10 may also include an optional recuperator 50 comprising a heat exchanger for transferring heat from the exhaust gases of the engine 52 to the compressed air 54 discharged from the compressor 22 before the air is supplied to the combustor. The recuperator captures part of the waste heat that would otherwise be lost and uses it to preheat the combustion air and, thereby, increase the overall efficiency of the engine, as is known in the art. As indicated, the system 10 also includes power electronics. In the illustrated embodiment, the power electronics comprise an AC / DC converter 60 and a DC / AC or inverter module 70. The AC / DC converter 60 can comprise any suitable converter that can be operated to convert the alternating current. produced by the generator, which may vary in frequency as the generator speed varies, in a non-alternating direct current and, additionally, which may be operated in a current control mode to control the direct current level, independently of the characteristics of the alternating input current (within certain limits). Said active current control is generally based on pulse width modulation (PWM) schemes that use semiconductor switching devices that perform high frequency switching operations and allow current to flow effectively only during a portion of each period of the waveform of the input current. This "window of time" during which the current is allowed to pass can be varied in terms of duration, so that the "average" current output from the converter is varied. The DC / AC module or inverter 70 then processes the output of the AC / DC converter 60, so as to synthesize an alternating output current at a fixed frequency. In many countries, the standard frequency of the main derivation is 60 cycles per second, while in other countries it is 50 cycles per second. The output frequency of the inverter is selected to coincide with the standard frequency of the main branch used in the particular location in which the system 10 is to be operated. The system 10 also includes a series of sensors connected to the control system 40 for measuring different parameters. For example, an output power meter 72 is arranged to measure how much electrical power is being managed by the system. One or more motor sensors 74 monitor one or more variable thermodynamics associated with the motor cycle. Variable thermodynamics are used to determine when the engine is operating on its "map", that is, if the engine is operating at or near its design point or if it is operating outside of it. For example, a turbine inlet temperature sensor can be used to measure the turbine inlet temperature. As indicated above, the turbine inlet temperature represents the peak temperature of the operating liquid in the engine and generally correlates with the overall efficiency of the engine. Therefore, by measuring the turbine inlet temperature along with other parameters, it is possible to deduce a relative thermodynamic efficiency of the engine. A sensor 76 measures an inlet temperature to the recuperator 50 in the exhaust gas flow. Under conditions of partial load, if the engine is not controlled properly, the temperature of entry to the recuperator could exceed the maximum level dictated by the material limits. In accordance with it, the control system is advantageously connected with the sensor 76 to monitor the inlet temperature of the recuperator, while the control system adjusts the air flow through the motor to prevent the temperature from exceeding the material limit, at the same time that the turbine inlet temperature is kept as high as possible within this additional restriction. It may not be necessary to actually deduce a relative thermodynamic efficiency, but merely to measure one or more parameters that are indicative of the relative efficiency or operating condition of the engine. For example, as noted, it is known that, for a given power output of the motor (and, therefore, a given power output from the generator measured with the energy meter 72), the efficiency of the motor is generally optimize by maximizing the turbine inlet temperature. Accordingly, the control of the fuel / air ratio, by controlling the air flow rate, can be carried out in such a way as to maximize the turbine inlet temperature, within the permitted limits. More particularly, the materials of the turbine inlet nozzles have a maximum allowed temperature that must not be exceeded, in order to preserve a sufficient force and integrity of the material to avoid the failure of the parts. At a 100 percent load design point, the engine would generally be designed so that the turbine inlet temperature is at or near this maximum allowable temperature. For lower load conditions, the air flow can be controlled in such a way that the turbine inlet temperature does not fall substantially below that at the design point. When the system includes a recuperator 50, consideration of the material limits in the recuperator may require a departure from an operating mode of this constant turbine inlet temperature. More particularly, under very low partial load conditions, if the turbine inlet temperature were maintained at the same level as the 100% load point, the temperature of the exhaust gases entering the recuperator could exceed a value maximum allowed dictated by the material limits of the recuperator. Accordingly, in accordance with the invention, under said conditions, the speed of the generator can be controlled so as to control the flow of air through the engine (while simultaneously controlling the flow of fuel to the engine). ), so as to control the fuel / air ratio in such a way that the turbine inlet temperature is allowed to fall below the temperature corresponding to the 100 percent load operation condition. In this way, it can be avoided that the temperature of the exhaust gases entering the recuperator exceeds the predetermined maximum allowed value. Therefore, for example, the control system 40 may have stored in the memory a predetermined program of turbine inlet temperature versus a relative generator load. The relative generator load, which is reflected in the energy output measured by the energy meter 72, generally indicates the relative engine load and, therefore, provides an indication of when the engine is operating on its map. An appropriate control algorithm can be used by the control system 40 to control the air flow (by controlling the speed of the generator in some suitable way, such as by controlling the DC current of the AC / DC converter 60) , in such a way as to cause the turbine inlet temperature to coindicate substantially with the value dictated by the predetermined program. This is merely a simplified example of a possible control scheme, while other schemes in accordance with the invention may be used. Figure 2 shows that said turbine inlet temperature versus the relative generator load program could be seen as, and compares different temperatures at different points in the system 10 (solid lines), with existing temperatures that would exist if a type of control approach of the prior art were taken (dashed lines). According to the invention, under a relative generator load value of 100 percent (that is, the design point for the engine), the turbine inlet temperature is basically equal to a maximum turbine inlet temperature allowed of about 1200 K. The turbine inlet temperature is maintained at this value with respect to a relative generator load of about 40 percent. In contrast, in the control approach of the prior art, the turbine inlet temperature decreases steadily as the load drops below 100 percent. As a consequence, with the same relative load, the overall efficiency of the motor is greater for the control scheme according to the invention than for the control scheme of the prior art.

With a relative load of 40 percent, it can be observed that the turbine outlet temperature (which is basically equal to the inlet temperature of the recuperator) has been increased to the maximum allowable temperature of the recuperator of approximately 900 K. With even more loads If the turbine inlet temperature remained at approximately 1200 K, the turbine outlet temperature would exceed the maximum allowable temperature of the recuperator. Accordingly, according to the invention, the turbine inlet temperature is allowed to fall below 1200 K. Another factor that can influence the control program arises when the combustor 28 is a catalytic combustor. As indicated, catalytic combustors have a minimum inlet temperature that must be maintained in order to maintain the catalytic reaction. In the control approach of the prior art, it can be seen in FIG. 2 that, below a relative load of about 50 percent, the inlet temperature of the combustor falls below this minimum temperature of about 800 K. However, in accordance with the invention, the inlet temperature of the combustor It rises from approximately 800 K at the 100 percent load point to approximately 860 K at the 40 percent load point. Below the 40 percent load, the inlet temperature of the combustor remains approximately constant at about 860 K. Therefore, the invention allows efficiency improvements to be made under partial load conditions, at the same time it also allows the operation of the catalytic combustor in all the operation points. Figure 3 illustrates how the fuel / air ratio behaves both in the control approach of the invention using the air flow control and in the control approach of the prior art that does not use airflow control. In the case of flow control, the fuel / air ratio is generally considerably higher under partial load conditions than in the prior art method. The higher proportion of fuel / air with flow control reflects the fact that air flow is lower in the control approach of the prior art. From a 100 percent load down to a 40 percent load, the fuel / air ratio that uses flow control is reduced at a relatively low rate. The result is that the turbine inlet temperature is basically constant, as already indicated in figure 2. Below a load of 40 percent, the ratio of fuel / air with flow control is allowed to be reduced to a substantially high rate. From Figure 2, it will also be noted that the combustor entry temperature is generally higher in the control approach of the invention than in the prior art approach. Advantageously, a higher fuel / air ratio and a higher combustor inlet temperature generally favor lower emissions for low emission pre-mixed combustors.

The control scheme described so far has assumed that the turbine inlet temperature is directly measured and used as a control parameter. However, in some cases, it may not be practical to measure the turbine inlet temperature due to the extreme use environment in which a turbine inlet temperature sensor would have to operate. Therefore, alternatively, it is possible to measure other thermodynamic variables in the motor cycle and deduct the turbine inlet temperature based on cycle calculations. As yet another alternative, the control system could store a program of a suitable control parameter (e.g., air flow of the motor) versus a relative generator load and the variable thermodynamics could be measured by deducting the control parameter. The control system would then operate the actual control parameter (ie, deduced) to be basically equal to the programmed value. The particular control method that is used and the parameters measured to perform the method are not essential. The basic concept of the invention involves controlling the air flow through the engine as a means of improving or optimizing the overall efficiency of the engine for any given power output of the generator system 10. At the same time, in an operational mode of tracking of charge, the energy output of the generator system 10 must be controlled to match the energy demanded by the load. The energy output is primarily a function of the fuel flow. Accordingly, in a charge tracking mode, the control system 40 simultaneously controls the air flow, as described above, while also controlling the power output (measured by the energy meter 72) for that matches the demand. The load tracking control schemes are well known and, therefore, are not described further herein. Depending on the particular application, the system 10 may also be operated in modes other than load tracking. In such cases, the same type of airflow control already described would continue to be used. The system 10 described above has a single coil turbine motor 20. However, the invention is not limited to any particular type of air breathing motor. Multi-wind turbine engines, turbine engines having an energy-free turbine, rotary combustion engines (e.g., Wankel), reciprocating piston engines and others can be used. In each case, the air flow through the motor is controlled by controlling the speed of the generator. The generator 30 can be of different types, including permanent magnet generators and winding generators. The above-described embodiment of system 10 presupposed that the generator is a permanent magnet generator where there is no excitation system. On the other hand, in the case of a winding generator, the generator requires an excitation system 80 (Figure 1) to supply an excitation current to the rotor windings, as is known in the art. For example, the excitation system may comprise a small generator mounted on the same axis as the rotor or mechanically coupled (e.g., with a conveyor belt) to the rotor shaft. Regardless of the type of generator, the invention involves electrically controlling the speed of the generator, so as to control the air flow through the engine, thus optimizing the efficiency of the engine and possibly achieving other effects indicated above. In the case of a permanent magnet generator, the control of the generator is achieved by controlling the AC / DC converter or rectifier 60 as already described. In the case of a winding generator, a series of control schemes is possible. In one scheme, the control system 40 controls the excitation system 80 (via the control line 82) to regulate the speed of the generator. The conversion of AC / DC and DC / AC may not be necessary and, instead, the AC / AC converter could be used to synthesize the AC output current at the desired frequency for supply to the load. Alternatively, the AC / DC and DC / AC converters could be used as described above, in which case the AC / DC converter does not have to be controlled in terms of current, given that the regulation of the generator speed is done by controlling the excitation system. In another scheme, the control of the generator speed could be achieved through a combination of controlling the excitation system and controlling the AC / DC converter. Another scheme is to control the speed of the generator exclusively through the control of the AC / DC converter, as already described. The details of how the generator speed is controlled are not essential to the invention and different schemes can be used to achieve this in accordance with the invention. Advantageously, the invention allows control of the thermodynamic cycle of a motor having a compressor of fixed geometry, turbine and combustor components. Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain, having the benefit of the teachings presented in the foregoing descriptions and the drawings associated therewith. Therefore, it should be understood that the inventions should not be limited to the specific embodiments described and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although some specific terms are used herein, they are used in a generic and descriptive sense only and not for limiting purposes.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A system for generating electric power for the supply to a load, comprising: an air breathing motor 20 that communicates mechanically with a movable shaft 24, the engine being structured and arranged to receive a mixture of air and fuel and submit to combustion the mixture, so that the mixture expands and creates mechanical energy that is used to drive the shaft; a fuel system 32 coupled with the engine and that can be operated to supply fuel to the engine, the fuel system having responsiveness to a fuel control signal to vary the fuel flow rate to the engine; at least one sensor 74 operable to measure at least one thermodynamic variable associated with the engine that is indicative of a relative thermodynamic efficiency of the engine; an electric generator 30 coupled with the shaft 24, so that the movement of the shaft 24 by the motor 20 causes the generator 30 to operate to create an alternating electric current, the motor 20, the shaft 24 and the generator 30 being connected to each other. so that a change in the speed of the generator 30 causes a corresponding change in the speed of the motor 20 and, therefore, a change in the air flow rate through the motor; a generator power sensor 72 that can be operated to measure the energy output of the generator 30; a load energy sensor that can be operated to measure the energy demanded by the load, characterized in that: a power electronics unit 60, 70 is coupled to the generator 30 to receive the alternating electrical current from that location, the power unit power electronics 60, 70 being operable to synthesize an alternating output voltage and current at a predetermined frequency and relative phase for supply to the load; and a controller 40 is operatively connected with the fuel system 32, with the at least one motor sensor 74, with the power electronics unit 60, 70, with the generator power sensor 72 and with the sensor of charge energy, the controller 40 being operable to control the fuel system 32 so as to cause the energy output of the system to basically coincide with the energy demanded by the load and, at the same time, to electrically control the generator 30 through the regulation of the power electronics unit 60, 70, so as to regulate the speed of the generator 30 and thereby control the air flow through the motor 20 such that the fuel ratio / air of the mixture subjected to combustion in the engine is controlled to substantially maximize the relative thermodynamic efficiency of the engine.

2. The system according to claim 1, further characterized in that the power electronics unit 60, 70 comprises an AC / DC module 60 structured and arranged to operate in relation to the alternating electric current of the generator 30, so that a direct current does not alternate to a non-alternating voltage, as well as a DC / AC module 70 structured and arranged to operate in relation to the non-alternating direct current, so that the alternating output current that is supplied is synthesized upon charging, the AC / DC module 60 having responsiveness to a current control signal to vary the level of the non-alternating direct current, independently of the alternating electrical current of the generator 30, the control system 40 being able to operate to supply the current control signal to the AC / DC module 60 to control the level of the direct current output by the AC / DC module 60 and continue thus rolling the generator speed.

3. The system according to claim 1, further characterized in that the generator 30 and the shaft 24 are rotatably movable.

4. The system according to claim 3, further characterized in that the motor 20 comprises a compression device 22 that can be operated to compress air and an energy device 26, 28 that receives the compressed air from the compression device 22 and the fuel from the fuel system 32 and submits to combustion the mixture of air and fuel to produce mechanical energy.

5. The system according to claim 4, further characterized in that it comprises a heat exchanger 50 arranged to receive the compressed air of the compression device 22 and the exhaust gases of the energy device 26, 28, the heat exchanger 50 causing the transferring heat from the exhaust gases to the compressed air, so that the compressed air is preheated before combustion in the energy device 26, 28.

6. The system according to claim 5, further characterized in that the device of energy 26, 28 includes a combustor 28 in which the air-fuel mixture is combusted to produce hot gases, as well as an expansion device 26 for expanding the hot gases so that mechanical energy is produced.

7. The system according to claim 6, further characterized in that the expansion device 26 comprises a turbine.

8. The system according to claim 7, further characterized in that the turbine 26 is a turbine of fixed geometry.

9. The system according to claim 6, further characterized in that the compression device 22 is a compressor of fixed geometry.

10. The system according to claim 6, further characterized in that the combustor 28 is a combustor of fixed geometry.

11. The system according to claim 6, further characterized in that the combustor 28 comprises a catalytic combustor.

12. - The system according to claim 11, further characterized in that it comprises a sensor that can be operated to measure a variable indicative of the inlet temperature of the combustor and because the controller 40 is connected to said sensor and can be operated to control the flow of air through the motor 20 in such a way that the inlet temperature of the combustor is maintained above a predetermined minimum temperature required for the catalytic operation.

13. The system according to claim 12, further characterized in that it comprises a sensor 76 associated with the heat exchanger 50 that can be operated to measure a variable indicative of a temperature of the exit gases that are introduced into the heat exchanger 50. and in that the controller 40 is connected to said sensor 76 associated with the heat exchanger 50 and can be operated to control the flow of air through the motor 20 to maintain the temperature of the exit gases which are introduced into the heat exchanger 50 by below a predetermined maximum temperature.

14. The system according to claim 1, further characterized in that the generator 30 is a winding generator.

15. The system according to claim 14, further characterized in that it comprises an excitation system 80 that can be operated to excite the generator 30.

16. - The system according to claim 15, further characterized in that the control system 40 can be operated to control the excitation system 80, so that the speed of the generator is electrically controlled and the air flow rate is controlled thereby.

17. A method for controlling an electric generator system having an air breathing motor 20 that communicates mechanically with a movable shaft 24, the engine 20 being structured and arranged to receive a mixture of air and fuel and combust the mixture, so that the mixture expands and creates mechanical energy that is used to control the shaft 24, the system having a fuel system 32 coupled with the engine 20 and which can be operated to supply fuel to the engine 20, the system of fuel 32 having responsiveness to a fuel control signal for varying the fuel flow to the engine 20, the system having an electric generator 30 coupled to the shaft 24, so that the movement of the shaft 24 by means of the motor 20 causes the generator 30 to operate to create an alternating electric current, wherein the motor 20, the shaft 24 and the generator 30 are connected so that a change in the The speed of the generator 30 causes a corresponding change in the speed of the motor 20 and, therefore, a change in the air flow through the motor 20, as well as where the electrical power output of the system is basically determined by the flow rate of fuel to the engine 20, the method comprising the steps of: determining an energy demanded by the load; measuring at least one thermodynamic variable associated with the motor 20 which is indicative of a relative thermodynamic efficiency of the motor 20; and controlling the fuel supply system 32 to supply fuel to the engine at a controlled fuel flow rate, so that the electrical power output of the system basically matches the energy demanded by the load; characterized in that the system includes a power electronics unit 60, 70 coupled with the generator 30 to receive the alternating electrical current from that location and can be operated to synthesize an alternating output voltage and current at a predetermined frequency and relative phase for the supply to the load; and the air flow rate through the motor 20 is controlled independently of the electrical power output of the electrically controlled system the speed of the generator 30 through the regulation of the power electronics unit 60, 70, so as to control the fuel / air ratio of the mixture subjected to combustion in the engine 20, in such a way that the thermodynamic efficiency of the engine 20 is substantially optimized, at the same time as it basically coincides with the energy sued for the load.

18. The method according to claim 17, further characterized in that the alternating electric current of the generator 30 is converted into an AC / DC module 60 to a direct current not alternating to a non-alternating voltage, while the direct current no alternating AC / DC module 60 is converted into a DC / AC 70 module to synthesize the alternating output current that is supplied to the load, the AC / DC module 60 having responsiveness to a current control signal to vary the level of the non-alternating direct current independently of the alternating electric current of the generator 30, as well as because the step of controlling the air flow comprises actively controlling the non-alternating direct current of the AC / DC module. 60 of the power electronics unit 60, 70, so as to alter the speed of the generator 30 and, therefore, the air flow rate.

19. The method according to claim 17, further characterized in that the motor 20 comprises a turbine engine having a compressor 22 for compressing the air, a combustor 28 for combustion of the mixture of air and fuel to produce hot gases and a turbine 26 for expanding the hot gases and because optimizing the thermodynamic efficiency of the engine 20 comprises making a turbine inlet temperature basically match a predetermined value.

20. The method according to claim 19, further characterized in that the combustor 28 comprises a catalytic combustor and comprises the steps of: measuring a variable indicative of an inlet temperature to the combustor 28; and controlling the flow of air through the motor 20 such that the inlet temperature of the combustor is maintained above a predetermined minimum temperature required for the catalytic operation.